The present invention relates to a micro electromechanical system (MEMS) microphone, a manufacturing method thereof, and an electronic device containing the same.
MEMS microphones are one of the most successful MEMS products, which are compatible with existing integrated circuits manufacturing techniques. MEMS microphones can be manufactured using process techniques of semiconductor devices. Thanks to the continuous development of CMOS process technology, MEMS microphones can be made very small and have been used in a variety of wearable communication devices including mobile phones, tablet PCs, notebooks, still cameras, video cameras, hearing aids and others.
MEMS microphones can generally be capacitive microphones including a vibrating membrane (lower electrode) fixedly formed on a substrate and facing an opening disposed on a backside of the substrate, and a fixed plate (upper electrode) being suspended above the vibrating membrane. A sealed cavity is disposed between the vibrating membrane and the fixed plate. A MEMS microphone enables detection of a capacitive value change due to the displacement of the vibrating membrane in the sealed cavity, and the detected value change is then processed.
Current process techniques for manufacturing MEMS microphones employ wet etching, e.g., using a buffered oxide etch (BOE) process, to remove the silicon oxide (SiO2) to form a cavity, so that the membrane can vibrate in the cavity. The shape and volume of the cavity structure may affect the operation of the microphone. In general, silicon nitride (SiN) with good corrosion resistance can be used as a support for forming the cavity structure.
FIG. 1A is a cross-sectional view depicting a partial structure of an intermediate stage of a conventional microphone in a manufacturing method according to the prior art. Referring to FIG. 1A, a structure of a half of a conventional microphone is shown to include a substrate 100, a first silicon dioxide layer 101 on substrate 100, a first polysilicon layer 111 on first silicon dioxide layer 101, a second silicon dioxide layer 102 on first polysilicon layer 111, a second polysilicon layer 112 on second silicon dioxide layer 102, and a silicon nitride layer 140 overlying the substrate. Through-holes 130 are formed through silicon nitride layer 140 and second polysilicon layer 112 and extending to second silicon dioxide layer 102. A recess is formed in substrate 100 to expose first silicon dioxide layer 101. Next, a BOE etch process is performed on the silicon dioxide layers through the through-holes and the recess to form cavities, as shown in FIG. 1B.
In the above-described process, in the stepwise structure of the silicon nitride layer (as indicated by the dashed circle in FIG. 1B), in particular when the step height is greater than a certain thickness, the density of the silicon nitride growth is low in the step, so the silicon nitride can be easily removed in the BOE etch process, so that cracks will be formed, thereby significantly affecting the reliability of the device.
As described above, the prior art technique does not provide a crack-free silicon nitride layer when using a BOE process, so that the reliability of the microphone is adversely affected. Therefore, there is a need for a novel method for manufacturing a MEMS microphone that provides a step-shaped silicon nitride layer that is crack-free.